hello soma !
for video editing i use Adobe Premiere 6.5 and Sonic Foundry Vegas Video 4+DVD . they both have good audio editing features, but i find it a lot easier just extracting the audio from video and doing all the audio effects in Cool Edit Pro 2.1
Adobe has a steep learning curve, but it is the best. i recommend Cool Edit Pro 2.1 if your just doing audio editing.
it also has an AC3 Encoder for encoding to 5.1 surround sound, if you have a dvd burner.
regards
m8t